The vestibulo-ocular (VORs) are an essential component of the oculomotor system since they are fundamental for gaze stabilization during both angular (angular VORs) and linear (linear VORs) head movements. Damage to the vestibular system through disease or trauma can produce profound oculomotor deficits that are often difficult to resolve clinically. Vestibular disturbances are often accompanied by nystagmus, blurred vision, dizziness and spatial disorientation. Despite years of research regarding the neural mechanisms of angular VOR function and disease states, very little is currently known about the linear VORs. Moreover, almost no information exists regarding the symptomology of otolith system damage and few, if any, practical diagnostic evaluations of otolith function are routinely performed in clinical today. The current proposal seeks to study the nature and function of the linear VORFs in primates and to investigate the deficits produced by cerebellar lesions and peripheral vestibular damage. The primary goal of these studies is to test quantitative predictions of a functional framework regarding the bilateral organization of the linear VORs across a wide stimulus repertoire in awake rhesus monkeys trained to fixate targets at different distances and vertical/horizontal eccentricities. Precisely calibrated binocular three-dimensional eye movements will be recorded during both lateral and fore-act linear motion consisting of either steady-state sinusoidal or transient stimulus profiles. Data obtained from normal animals will be quantitatively compared to the eye movements generated during functional ablation of the most irregularly firing vestibular afferents, as well as both acutely and chronically after unilateral labyrinthectomy, selective semicircular canal plugging and cerebellar lesions. The results will provide for the first time quantitative data and models regarding the bilateral neural organization of the linear VORs as well as identify practical clinical tests of peripheral and central otolith-ocular function.